1. Field
Disclosed embodiments relate to a mold boring method, a mold boring tool, and a mold boring apparatus for making a hole in a mold such as a degassing hole in a mold, particularly, a sand mold.
2. Related Art
There is conventionally known a method of making a hole such as degassing hole in a mold, i.e., sand mold, by forming a punching hole by moving a punching pin (degassing pin or needle) by using a cylinder assembly, for example, as disclosed in Japanese Patent Laid-Open Publication No. 11-10284 (Patent Document 1) or a method of making a hole by rotating a drill.
FIG. 6B shows one example representing the punching method by using the punching (boring) pin to form the degassing hole in the mold. In this method, when a punching pin 101 is inserted into sand 103 of a mold 102 as illustrated in FIG. 6B, an excessive compressive force P acts on the sand 103 in the mold 102 because the volume of the mold 102 does not change. Consequently, when the punching pin 101 passes through the mold 102, the compressive force P concentrates on a punching (boring) penetration boundary side 104 of the mold 102, which may result in breaking of the mold 102 at the penetration boundary side 104, and broken sand 105 may drop off. Accordingly, if punched (bored) holes are formed at points adjacent to each other, the holes may be continuously connected to each other, and thus, will not attain function as holes. In addition, if a hole is formed near a sprue (pouring gate), there is a possibility of breaking or collapsing the sprue.
Furthermore, if an action of the punching pin 101 applies an excessive compressive force P to the sand 103 of the mold 102, a reaction force thereof may make the punching pin 101 more deformable, and in such case, it becomes difficult to form a hole having a small diameter.
On the other hand, according to the cutting method by using the drill to form the degassing hole in the mold, a large load is applied to the drill, which may break the drill, so that it becomes difficult to form a hole having a small diameter with high precision. Moreover, a rotating mechanism for rotating the drill is required, which will result in an increase of size of entire unit or apparatus.